The present disclosure relates to electric power conversion, and more particularly to DC power to AC power conversion using multilevel inverters and methods of controlling multilevel inverters to convert DC power into AC power.
Power converters are commonly employed in a variety of applications to convert direct current (DC) power into alternating current (AC) power and vice versa. A converter for AC power to DC power conversion is generally referred to as a rectifier while a converter for DC power to AC power conversion is typically referred to as an inverter. Employment of active components in the converter, such as transistors, allows for regulation of the voltages generated by the converter. Multilevel converter architectures allow for employment of active components with ratings below that of the converter, typically by use of a multilevel DC link.
Multilevel DC links generally include a positive lead, a DC midpoint lead, and negative lead with balancing capacitors connected in series between the DC midpoint lead, positive lead, and negative lead. The DC midpoint voltage is typically maintained at 0 volts DC with respect to ground, allowing connection of the active components to one of the positive and negative leads and the midpoint lead. While this can allow the active components to be rated at one-half the DC link voltage, cycling of the active components typically induces ripple in the DC midpoint voltage. In some applications, such as four (4) wire inverters, large single phase loads or short circuits can induce ripple in the DC midpoint voltage such that upwards of 100% of the DC link voltage is applied to one of the two series connected link capacitors, potentially damaging the link capacitor and/or active components of the converter due to the associated voltage stress.
Such conventional power converters and power conversion methods have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved power converters and power conversion methods. The present disclosure provides a solution for this need.